<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        .demo {
            width: 400px;
            height: 300px;
            background-color: pink;
            margin: 100px auto;
            position:relative;
        }
    </style>
     <script src="js/jquery-1.11.3.min.js"></script>
         <script type="text/javascript">
             $(function() {
                 $("div").on("mouseenter mouseleave",function(e) {
                     var w = $(this).width(); // 得到盒子宽度
                     var h = $(this).height();// 得到盒子高度
                     var x = (e.pageX - this.offsetLeft - (w / 2)) * (w > h ? (h / w) : 1);
                     // 获取x值
                     var y = (e.pageY - this.offsetTop - (h / 2)) * (h > w ? (w / h) : 1);
                     // 获取y值
                     var direction = Math.round((((Math.atan2(y, x) * (180 / Math.PI)) + 180) / 90) + 3) % 4; //direction的值为“0,1,2,3”分别对应着“上，右，下，左”
                     // 将点的坐标对应的弧度值换算成角度度数值
                     var dirName = new Array('上方','右侧','下方','左侧');
                     if(e.type == 'mouseenter'){
                         $(this).html(dirName[direction]+'进入');
                     }else{
                         $(this).html(dirName[direction]+'离开');
                     }
                 });
             })
     </script>
</head>
<body>
<div class="demo"></div>
</body>
</html>
